1/* $NetBSD: ssh-keysign.c,v 1.24 2022/10/05 22:39:36 christos Exp $ */ 2/* $OpenBSD: ssh-keysign.c,v 1.71 2022/08/01 11:09:26 djm Exp $ */ 3 4/* 5 * Copyright (c) 2002 Markus Friedl. All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28#include "includes.h" 29__RCSID("$NetBSD: ssh-keysign.c,v 1.24 2022/10/05 22:39:36 christos Exp $"); 30#include <sys/types.h> 31 32#ifdef WITH_OPENSSL 33#include <openssl/evp.h> 34#endif 35 36#include <fcntl.h> 37#include <paths.h> 38#include <pwd.h> 39#include <stdarg.h> 40#include <stdio.h> 41#include <stdlib.h> 42#include <string.h> 43#include <unistd.h> 44#include <errno.h> 45 46#include "xmalloc.h" 47#include "log.h" 48#include "sshkey.h" 49#include "ssh.h" 50#include "ssh2.h" 51#include "misc.h" 52#include "sshbuf.h" 53#include "authfile.h" 54#include "msg.h" 55#include "canohost.h" 56#include "pathnames.h" 57#include "readconf.h" 58#include "uidswap.h" 59#include "ssherr.h" 60 61extern char *__progname; 62 63static int 64valid_request(struct passwd *pw, char *host, struct sshkey **ret, char **pkalgp, 65 u_char *data, size_t datalen) 66{ 67 struct sshbuf *b; 68 struct sshkey *key = NULL; 69 u_char type, *pkblob; 70 char *p; 71 size_t blen, len; 72 char *pkalg, *luser; 73 int r, pktype, fail; 74 75 if (ret != NULL) 76 *ret = NULL; 77 if (pkalgp != NULL) 78 *pkalgp = NULL; 79 fail = 0; 80 81 if ((b = sshbuf_from(data, datalen)) == NULL) 82 fatal_f("sshbuf_from failed"); 83 84 /* session id */ 85 if ((r = sshbuf_get_string(b, NULL, &len)) != 0) 86 fatal_fr(r, "parse session ID"); 87 if (len != 20 && /* SHA1 */ 88 len != 32 && /* SHA256 */ 89 len != 48 && /* SHA384 */ 90 len != 64) /* SHA512 */ 91 fail++; 92 93 if ((r = sshbuf_get_u8(b, &type)) != 0) 94 fatal_fr(r, "parse type"); 95 if (type != SSH2_MSG_USERAUTH_REQUEST) 96 fail++; 97 98 /* server user */ 99 if ((r = sshbuf_skip_string(b)) != 0) 100 fatal_fr(r, "parse user"); 101 102 /* service */ 103 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 104 fatal_fr(r, "parse service"); 105 if (strcmp("ssh-connection", p) != 0) 106 fail++; 107 free(p); 108 109 /* method */ 110 if ((r = sshbuf_get_cstring(b, &p, NULL)) != 0) 111 fatal_fr(r, "parse method"); 112 if (strcmp("hostbased", p) != 0) 113 fail++; 114 free(p); 115 116 /* pubkey */ 117 if ((r = sshbuf_get_cstring(b, &pkalg, NULL)) != 0 || 118 (r = sshbuf_get_string(b, &pkblob, &blen)) != 0) 119 fatal_fr(r, "parse pk"); 120 121 pktype = sshkey_type_from_name(pkalg); 122 if (pktype == KEY_UNSPEC) 123 fail++; 124 else if ((r = sshkey_from_blob(pkblob, blen, &key)) != 0) { 125 error_fr(r, "decode key"); 126 fail++; 127 } else if (key->type != pktype) 128 fail++; 129 130 /* client host name, handle trailing dot */ 131 if ((r = sshbuf_get_cstring(b, &p, &len)) != 0) 132 fatal_fr(r, "parse hostname"); 133 debug2_f("check expect chost %s got %s", host, p); 134 if (strlen(host) != len - 1) 135 fail++; 136 else if (p[len - 1] != '.') 137 fail++; 138 else if (strncasecmp(host, p, len - 1) != 0) 139 fail++; 140 free(p); 141 142 /* local user */ 143 if ((r = sshbuf_get_cstring(b, &luser, NULL)) != 0) 144 fatal_fr(r, "parse luser"); 145 146 if (strcmp(pw->pw_name, luser) != 0) 147 fail++; 148 free(luser); 149 150 /* end of message */ 151 if (sshbuf_len(b) != 0) 152 fail++; 153 sshbuf_free(b); 154 155 debug3_f("fail %d", fail); 156 157 if (!fail) { 158 if (ret != NULL) { 159 *ret = key; 160 key = NULL; 161 } 162 if (pkalgp != NULL) { 163 *pkalgp = pkalg; 164 pkalg = NULL; 165 } 166 } 167 sshkey_free(key); 168 free(pkalg); 169 free(pkblob); 170 171 return (fail ? -1 : 0); 172} 173 174int 175main(int argc, char **argv) 176{ 177 struct sshbuf *b; 178 Options options; 179#define NUM_KEYTYPES 5 180 struct sshkey *keys[NUM_KEYTYPES], *key = NULL; 181 struct passwd *pw; 182 int r, key_fd[NUM_KEYTYPES], i, found, version = 2, fd; 183 u_char *signature, *data, rver; 184 char *host, *fp, *pkalg; 185 size_t slen, dlen; 186 187#ifdef __OpenBSD__ 188 if (pledge("stdio rpath getpw dns id", NULL) != 0) 189 fatal("%s: pledge: %s", __progname, strerror(errno)); 190#endif 191 192 /* Ensure that stdin and stdout are connected */ 193 if ((fd = open(_PATH_DEVNULL, O_RDWR)) < 2) 194 exit(1); 195 /* Leave /dev/null fd iff it is attached to stderr */ 196 if (fd > 2) 197 close(fd); 198 199 i = 0; 200 /* XXX This really needs to read sshd_config for the paths */ 201 key_fd[i++] = open(_PATH_HOST_DSA_KEY_FILE, O_RDONLY); 202 key_fd[i++] = open(_PATH_HOST_ECDSA_KEY_FILE, O_RDONLY); 203 key_fd[i++] = open(_PATH_HOST_ED25519_KEY_FILE, O_RDONLY); 204 key_fd[i++] = open(_PATH_HOST_XMSS_KEY_FILE, O_RDONLY); 205 key_fd[i++] = open(_PATH_HOST_RSA_KEY_FILE, O_RDONLY); 206 207 if ((pw = getpwuid(getuid())) == NULL) 208 fatal("getpwuid failed"); 209 pw = pwcopy(pw); 210 211 permanently_set_uid(pw); 212 213#ifdef DEBUG_SSH_KEYSIGN 214 log_init("ssh-keysign", SYSLOG_LEVEL_DEBUG3, SYSLOG_FACILITY_AUTH, 0); 215#endif 216 217 /* verify that ssh-keysign is enabled by the admin */ 218 initialize_options(&options); 219 (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw, "", "", 220 &options, 0, NULL); 221 (void)fill_default_options(&options); 222 if (options.enable_ssh_keysign != 1) 223 fatal("ssh-keysign not enabled in %s", 224 _PATH_HOST_CONFIG_FILE); 225 226#ifdef __OpenBSD__ 227 if (pledge("stdio dns", NULL) != 0) 228 fatal("%s: pledge: %s", __progname, strerror(errno)); 229#endif 230 231 for (i = found = 0; i < NUM_KEYTYPES; i++) { 232 if (key_fd[i] != -1) 233 found = 1; 234 } 235 if (found == 0) 236 fatal("could not open any host key"); 237 238#ifdef WITH_OPENSSL 239 OpenSSL_add_all_algorithms(); 240#endif 241 242 found = 0; 243 for (i = 0; i < NUM_KEYTYPES; i++) { 244 keys[i] = NULL; 245 if (key_fd[i] == -1) 246 continue; 247 r = sshkey_load_private_type_fd(key_fd[i], KEY_UNSPEC, 248 NULL, &key, NULL); 249 close(key_fd[i]); 250 if (r != 0) 251 debug_r(r, "parse key %d", i); 252 else if (key != NULL) { 253 keys[i] = key; 254 found = 1; 255 } 256 } 257 if (!found) 258 fatal("no hostkey found"); 259 260 if ((b = sshbuf_new()) == NULL) 261 fatal("%s: sshbuf_new failed", __progname); 262 if (ssh_msg_recv(STDIN_FILENO, b) < 0) 263 fatal("%s: ssh_msg_recv failed", __progname); 264 if ((r = sshbuf_get_u8(b, &rver)) != 0) 265 fatal_r(r, "%s: buffer error", __progname); 266 if (rver != version) 267 fatal("%s: bad version: received %d, expected %d", 268 __progname, rver, version); 269 if ((r = sshbuf_get_u32(b, (u_int *)&fd)) != 0) 270 fatal_r(r, "%s: buffer error", __progname); 271 if (fd < 0 || fd == STDIN_FILENO || fd == STDOUT_FILENO) 272 fatal("%s: bad fd = %d", __progname, fd); 273 if ((host = get_local_name(fd)) == NULL) 274 fatal("%s: cannot get local name for fd", __progname); 275 276 if ((r = sshbuf_get_string(b, &data, &dlen)) != 0) 277 fatal_r(r, "%s: buffer error", __progname); 278 if (valid_request(pw, host, &key, &pkalg, data, dlen) < 0) 279 fatal("%s: not a valid request", __progname); 280 free(host); 281 282 found = 0; 283 for (i = 0; i < NUM_KEYTYPES; i++) { 284 if (keys[i] != NULL && 285 sshkey_equal_public(key, keys[i])) { 286 found = 1; 287 break; 288 } 289 } 290 if (!found) { 291 if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, 292 SSH_FP_DEFAULT)) == NULL) 293 fatal("%s: sshkey_fingerprint failed", __progname); 294 fatal("%s: no matching hostkey found for key %s %s", __progname, 295 sshkey_type(key), fp ? fp : ""); 296 } 297 298 if ((r = sshkey_sign(keys[i], &signature, &slen, data, dlen, 299 pkalg, NULL, NULL, 0)) != 0) 300 fatal_r(r, "%s: sshkey_sign failed", __progname); 301 free(data); 302 303 /* send reply */ 304 sshbuf_reset(b); 305 if ((r = sshbuf_put_string(b, signature, slen)) != 0) 306 fatal_r(r, "%s: buffer error", __progname); 307 if (ssh_msg_send(STDOUT_FILENO, version, b) == -1) 308 fatal("%s: ssh_msg_send failed", __progname); 309 310 return (0); 311} 312